Communication system



July 1, 1941. c, R. DOT 2,247,909

COMMUNICATION SYSTEM 3 Sheets-Shem FIG. 1.

Filed Dec. 5, 1939 MU 1 ALI Plus: 2 a il /55] +zsn lNVENTOR AT'ToRNEY Julyl, 1941. c. R. DOTY 2,247,909

COMMUNICATION SYSTEM 3 Sheets-Sheet 2 MRI 7' Filed Dec. 5. 1939 A I TRIA lglVf-INT BY 4,

ATTORNEY July 1, 1941. c, DQTY 2,247,

COMMUNICATION SYSTEM v Filed Dec. 5, 1939 whens-sheet 3 FIG-4.

. I Phase 1 I v J Phase 2 A v 1 Phase, 3 4)\ i I A I Phdse 4 I I v 4 Phase 5 A I i 1 A Phase 6 A i A Phase 1 I I I 1 m Phase 8 J I I i INVENTOR BY m ATTORNEY Patented July 1, 1941 UNITE COMMUNICATION SYSTEM Charles R. Doty, Yonkers, N. Y., assignor to International Business Machin es Corporation} New York, N. Y., a corporation of New York Application December 5, 1939, Serial No. 301,568

3 Claims.

This invention relates to communication systems and, mor particularly, to two-way transmission systems comprising a plurality of startstop printers adapted for operation "over a single working channel.

It is the general object of the instant invention to provide an improved system wherein the customary two wires connecting the transmitting and receiving portions of the system have their control properties and their transmission capacities greatly increased by means of phasesplitting, a factor whichpermits simultaneous operation of a plurality of start-stop printers at both stations with the same facility as though they were each connected by individual metallic circuits.

More specifically, it is proposed to send coded impulses of different phase relationship from each transmitter so as to permit receiving units to be selected for operation in accordance with the different phases of the impulses and thereby to provide lfor multiple unit control over a single working channel without signal interference.

According to the instant invention, a plurality of teletypewriter machines or the like are located at each end of a single transmission line and arranged for transmitting or receiving impulses corresponding to data. The circuit structure at each end of the line is similar and includes a phase transformer,- a plurality of electronic tubes and, of course, the machines themselves. Some of the electronic tubes act as transmission valves and others as receiving valves, one transmission valve and two receiving valves being associated with the transmitting unit and receiving unit, respectively, of each machine. The transmission valvesare each impressed with a different phase potential from the phase transformer. Each of these valves, however, remains inoperative insofar as the passage of impulses to the line is concerned until the transmitting unit of its associated machine is operated to initiate impulses corresponding to data. At such time, the tube passes current impulse waves of a particular phase which are then impressed on the transmission line. The receiving valves also have different phase potentials from the phase transformer impressed on them, the reception of impulses of a phase corresponding to the phase of the impressed potential causing the tube to pass current for operating the recording unit to record the data. By virtue of the fact that the impulses transmitted from each machine at one end of the line to a corresponding machine at the other end of the line have different phase characteristics. there is no signal interference. Sending over the line in the opposite direction is efiected in the same way, each wave impulse identifying by its phase the machine which effected its transmission. Thus. the proposed system presents, in effect, an improved method of multiplexing by multiphasing.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Figs. 1 and 2 are wiring diagrams of the primary and secondary stations, respectively.

Fig. 3 is adiagram of thephase connections of a phase transformer from which eight different phases may be taken.

Figs 4, 4a, and 4b taken together, show the effect of the rectifying action of the discharge tube connected to one of the phases of the transformer;

Fig. 5 illustrates the manner in which a plurality of signals may be impressed on a line at the same time without interference.

Referring now to the drawlngs,'and particularly to Figs. 1 and 2, three main operating units of a standard start-stop teletypewriter are represented symbolically by the reference characters M, T, and P in a conventionally diagrammatic form. M refers to a motor which may be governor controlled or synchronous; T refers toa set of cam operated transmitting contacts which are arranged to close at differential times to initiate coded combinations of impulses corresponding todata characters, and P refers to a signal magnet which operates in response to signals from the transmission line and which controls any well-known mechanism (not shown) for effecting selective character printing. To the standard arrangement has been added two sets of transfer contacts bearing the reference characters To and Th at each machine station, and these contacts are caused to transfer simultaneously with the opening of the normally closed set of teletypewriter line current contacts Ta and to again assume the position shown when the latter contacts are again closed so as to transmit the stop signal to the line. In operation, this system closely follows standard start-stop" printer operations which will now be reviewed briefly for the purpose of clarity.

Reference may be made to the Kinkhead Patent No. 1,795,652, dated March 10, 1931, for more detail as to the operation and structure of these systems.

In "start-stop" systems the receiving mechanisms are stopped at the end of each character cycle and are again started when the next letter is transmitted. All machines on the circuit must, therefore, operate at substantially the same speed in order that the sending and receiving mechanisms may always be in the same relative position. The motors which drive the units are equipped with governors which keep their speed within the required limits. When /closely regulated alternating current is available, synchronous motors may be used. In this system current is on the line during the normal idle condition of the machines and the transmitting is done by opening the circuit so that no current will flow, or closing it to cause current to flow. These electrical impulses are referred to as a code. The most commonly used code is known as the Baudot code, in which the same number of elements (ordinarily five) are transmitted for each character to be printed or function to be performed. These two conditions.

of current or no current in the line are known as marking and spacing impulses respectively.

In transmission, the depression of a typewriter key sets up a mechanical condition correspond- 7 ing to the code combination of the character to be printed or the function to be performed. The circuit condition of marking or spacing impulses at the time of transmission of the five selecting impulses, provides a total of 32 diflerent combinations.

Preceding the transmission of the five selecting elements is a period of no line current which is called the start time. This signalis sent automatically as soon as the sending mechanism is put into operation and initiates the operation of the receiving mechanism on all the receiving machines connected to the circuit. Following the selecting signals, current is again put on the line and this is called the stop impulse. This impulse arrests the operation of the receiving mechanism of all the receiving instruments connected to the circuit. In keyboard sending the maximum length of the stop impulse depends upon the time the operator hesitates between the striking of the individual keys of the teletypewriter.

Four sets of standard start-stop printer stations, represented generally by reference characters L! to L4, are shown in Fig. 1 and likewise four more designated Ri to R4 are set forth in Fig. 2. In order to facilitate describing the circuits in the explanation in the wiring diagram which is given hereinafter, the reference characters referred to in the preceding paragraph are provided with suffixes L or R, followed by a numeral 1 to 4, which allocate them to the particular machine stations Ll to L4 or Rl to R4 as the case may be. The mechanism at each machine station is similar and thus a description of the transmission of a signal from saymachine MLI and a reception of that signal on machine MRI will explain the principle of operation of the system.

The signal system employs a multi-phase principle comprising a plurality of signals which may be impressed on the transmission line simultaneously without interference, the different phases being devised from phase transformers at the primary and secondary stations in a manner which will now be described.

Referring to Fig. 3, it will benoted that the action of the phase transformer shown in that figure is to take single phase synchronous alternating current and sub-divide the same into as many equally spaced phases as may be required by the system. In the present embodiment eight such phases are arranged to be supplied by each transformer; Transformers of this type are provided at both primary and secondary stations and are adapted to be connected to various tube circuits at these stations for the purpose of supplying them with electrical energy of different phase relationships. The internal connections of the transformers are not shown but may be of the type explained in detail in U. S. Patent No. 2,153,178, to Clyde J. Fitch, dated April 4, 1939. The turns ratio of the windings are such that the voltage delivered across the free ends of the secondary circuits are equal. For purposes of illustration, eight such secondary circuits are provided and are designated PHI to PH8. Different phase sine wave currents are taken off the various phase connection outlets of the secondary transformer for transmitting purposes, but it is obvious that a plurality of, let us say, sixty cycle sine waves cannot be transmitted simultaneously over the working channel of a single network to effect the various required operations of the system. In order to overcome this difliculty, the wave shapes similar to that of a sine wave are changed to the forms illustrated in Fig. 5, one method of which will now be described.

Referring now to Fig. 4, a sinusoidal wave form of alternating current is shown and is similar to the current wave forms developed by each of the plurality of secondary circuits of the phase transformer. These sinusoidal current waves may then be impressed upon any type of full wave rectifier to change the shape of the current waves to conform to that shown in Fig. 4a which is representative of a pulsating current wave form. In turn, the rectified current wave may then be applied as follows: If the voltage rectified wave form shown in Fig. 4a is impressed on the grid of a thermionic tube, for example, and the voltage is sufficient to drive the tube far below its plate current cut-off point, the shape of the current wave in the plate circuit will be altered to conform to the shape shown in Fig. 4b. The characteristics of the circuits may be selected and adjusted so that the length of the base of the short impulses shown in Fig. 4b is approximately of the distance between the impulses. Of course, it is obvious that the particular wave shapes may vary according to the characteristics of the circuits employed, and it is very evident by the method just described or by the conversions based upon the same principles that many different shapes of the resultant current may be obtained. Accordingly, a preferred method is given.

In further explanation of the principle of wave conversion just described, this entire action may take place automatically in a single thermionic tube of a type well known in the art comprising a combination of a full wave rectifier and triode' in one envelope. The electrical connections for this type of tube may be as shown in the wiring diagrams for tubes DLI to DIA, DRI to DR, ELI to EL! and ER! to ERl. It will be noted that the alternating voltage of the sinusoidal wave is applied across a center tapped resistor 3| (see tube DLI in Fig. 1). In each of the tube circuits the wave shape of the current flowing through this resistor or the voltage across it assimilates a wave form similar to that shown in Fig. 4. A resistor 32 is connected between the cathode of the tube and the center tap of resistor 3|, the terminals of which are connected to the two rectifier plates 29, 30 of the said tube. Therefore, the wave shape of the rectified current through resistor 32 and the voltage across I this resistor become similar to that shown by the pulsating wave in Fig. 4a. The grid 38 of the tube may also be connected to the center tap of resistor 3|, the grid being normally at zero bias due to the fact that no current is passing through resistor 32. Then, the voltage across resistor 32 may be applied between the grid and cathode of said tube.

If the said voltage is of suflicient value, the tube may be driven far below its plate current cut-off point to obtain a plate current having the wave shape similar to that shown in Fig, 4b. This is impressed accordingly on a connected output circuit of the tube which will be described later in connection with the general circuits of the system. Any suitable form of direct current supply may be employed for supplying electrical energy to the plate circuit of the signaling tubes. The negative terminal or" the battery is connected directly to the cathode of the signaling tubes and current flows through the plate circuit upon operation of the various character sending key contacts in the circuit which will be described later. This current fiow lasts for only a comparatively short time, however, because the bias on the grid is not a constant factor, but varies in timed relationship with the frequency of the A. ,0. supply coming from the secondary of the phase trans former, The said supply is impressed upon the full wave rectifying portion of the tube. The rectified voltage impressed across resistor 32 immediately drives the grid sumciently negative to prevent further flow of plate current. Thus, the plate current is reduced to a substantially zero value. At such times when the rectified voltage passes through zero, a pulse is impressed upon the output circuit of they triode. This pulse is utilized as a signal and is sent from the transmitter to the receiver to eflect operation of the punch mechanism at the receiver.

From the foregoing description, it will be understood that, if eight separate phases spaced 22 electrical degrees apart are taken off the secondary phase transformer and connected to eight electrical circuits each embodying a tube of the type just described, so that the terminals of the separate resistors 3| are joined with the terminals of the secondary windings of each phase, eight series of short impulses similar to those illustratedin Fig. 5 may be generated. It will be noted that no two impulses overlap or occur at the same time, and therefore it is possible that all eight of these phases may be transmitted over a single carrier simultaneously. For the sake of simplicity in the wiring diagrams the terminals of the various tubes are not shown fully connected to the phase connections of the phase transformer, but the terminals of the tube are given a designation PHI to PHB to indicate with which of the phases it is connected.

Referring now to the receiving tubes ELI to EM and ERI to ERG, it will be noted that the circuits for these tubes are similar to the ones described above. Taking tube ELI as an example, it will be assumed that this tube is connected to phase PHZ of the transformer, and

that the grid 43 of this tube is connected in the cathode circuit of the tube and is arranged to be normally biased to cut-off. The negative battery BLB is connected to one side of a resistance r and a condenser-C, each of which leads to the cathode circuit of tube ELI and also to the grid 44 of tube ALI. Positive battery potential of battery BL2 is applied to the anode of tube ELI.

When a signal is received, it is impressed upon a high biased tube 51 and then sent through conductor 58 to the circuits embodying tube ELI. Condenser C becomes charged and thus controls the actuation of the grid 44 of an amplifying tube 1 ALI to which it is connected in such a manner that if the phase relationship of the signal is the same as PH2, the tube ALI is triggered oil and a virtually steady current flows through its plate circuit to eifect energization of the print selector magnet PLI. It will be noted that tube ALI, normally inoperative, becomes operative only upon reception of a signal of a phase corresponding .to PHZ. The signal phase and the tube circuit phase must agree in order that the amplifier tube ALI may be operated, since the bias placed on the grid of tube ALI by each of these supply sources individually is insuflicient to cause current flow through the windings of magusual teletype system. Likewise, machine ML! is sending impulses of phase PH3 continuously to a corresponding machine MR2 which, in turn,

sends continuous impulses of phase PH! over the line to machine ML2. Similarly, machines ML3 and MR3 send continuous impulses of phases PH5 and PHG, respectively, and machines ML and MR4 employ phases PH! and PHB, respectively.

The transmission of a. typical character from machine MLI to machine MRI will now be described, it being understood that the other machines, although working on different phases, employ the same operating principle.

If the operator at station LI depresses a character key for the purpose of transmitting the character A, for example, the TL'I contacts are operated selectively in such a manner as to produce a coded series of impulses to represent A." The opening of contacts TLIa stops the continuous series of impulses on phase PHI which releases the current from print selector magnet PRI (Fig. 2) and initiates a receiving cycle at that station. At the time contacts TLIa open, contacts 'I'Llg and TLIh transfer to shift the tubes ELI and ALI from phase PHZ to phase PHI,

so that the magnet PLI will be responsive to the same impulses (PHI) that are being transmitted to operate the magnet PRI at the receiving station RI. Assume the letter A to'be represented by impulses under control of contacts TLIb and TLIc. After contacts TLIa are open for a suflicient length of time to initiate the start signal,

traced as follows: from plus battery BLI, conductor 50, transformer winding 5|, conductor 52, contacts TLIb now closed, conductor 53, .plate and cathode tube DLI, conductor 54, to negative battery BLI. The same circuit is completed through TLIc when these contacts make, The pulses impressed upon transformer winding 5i are simultaneously impressed on the line winding 55 and another winding 56. The impulses impressed on winding '56 overcome the high bias on the grid of tube 5'! created by a battery BL3 in series with winding 56 and grid and cathode of the tube causing the latter to pass current through it. The anode of tube 57 is connected to the cathode of tube ELI through conductor 58. Negative battery BL5 is normally applied through conductor 58 and condenser C and resistance r in parallel to the cathode of tube ELI and'the grid of tube ALI. The plate of tube ELI is connected with positive battery BLZ through conductor 59. The cathode of tube ALI is connected by means of conductor BI with the positive battery BL5. The selection of tube ELI for operation was by virtue of the fact that this tube alone of the group of tubes ELI to EL4 was operating on phase PHI and the incoming impulses combined with the normal phase current from source PHI to provide a flow of current through tube ELI but not through the others which were operating on other phases. The condenser C and resistance r in parallel provide a time lag for the impulses impressed on the grid of tube ALI, so that these impulses may remain effective to overcome the bias on the grid 44 for a much longer period than would otherwise be the case, thus giving a sufficiently long impulse to insure the actuation of print selector magnet PLI connected in the plate circuit of tube ALI. The circuit for energizing magnet PLI is from positive battery BL4, conductor 60, magnet PLI, plate and cathode of tube ALI, conductor GI, to negative battery BL4.

The impulses impressed on the line through the medium 'of transformer winding 55 in the manner described above are received by transformer winding 62 (Fig, 2) and then impressed upon winding 63. Impulses from winding 63 overcome the bias caused by battery BR3 on the tube 64 to initiate the flow of current through the tube 64 as follows: positive side of battery BR2, conductor 68, plate and cathode of tube ERI, condenser C and resistance r in parallel, conductors 65, 66, plate and cathode of tube 64, conductor 81, to negative battery BR2. Since there is no transmission from machine MRI at station RI at this time, transfer contacts TRIg and TRIh are in normal position and tube ERI is working on phase PHI. Thus, the impulses from the line coincide in phase with the impulses from the phase transformer at the receiving station and reinforce them so as to cause operation of tube ERI. Amplifier tube ALI is now caused to operate in View of the reduction of the bias on its grid as tube ERI is operated. The circuit is traceable from positive side of battery BB4, conductor I0, print selector magnet PRI, plate and cathode of tube AI, conductor 69, to negative battery BR4. As previously explained in connection with the circuits in Fig. 1, condenser C and resistance 1" provide the necessary time lag to insure the full energization' of magnet PRI upon operation of tube ARI. The input circuit to tube ARI is from negative battery BR5, conductor 65, condenser C and resistance r in parallel, conductor II, grid and cathode of tube ARI, conductor 69, to positive battery BR5,

At the end of each character cycle, contacts TLIa at transmitting station LI again close t send continuous signals of phase PH I which holds the magnet PRI at the receiving station RI in a normally energized condition.

It will be appreciated that it is possible for all eight machines to be operating at the same time over a two wire network in the manner above described. All of the operations of the normal teletypewriter are maintained and each of the machines, when transmitting, monitors its own signals through the energlzation of the print selector magnets-to effect printing of characters represented by, those signals.

Although the wiring diagram shows machine MLI at one station connected for operation with machine MRI, ML2 with MR2 etc., it is to be understood that the wiring to the phase transformers could bez sogaltered at any time that the machines could cpoperate for both transmitting and receiving in widely different arrangements.

While there has been shown and described and pointed out the fundamental novel features of the invention as applied to a single modification, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In a communication system comprising a plurality of printing telegraph machines at each end of a common line, in combination, means at one end of said line comprising a plurality of primary sources of current of different phase characteristics, a wave modifying device for each of said sources, a plurality of sets of control contacts, one for each machine, individual means for differentially operating said contacts according to a preselected code, and circuit connections normally completed under control of said sets of contacts from predetermined ones of said sources of current through the related wave modifying means to the line to impress modified wave forms of carrier currents on said line of predetermined different phases to represent the different machines, and means at the other end of the common line comprising a plurality of secondary sources of current of different phase characteristics corresponding to the phases of the aforementioned primary sources of current, an electronic valve connected to each of the secondary sources, a. plurality of printing control magnets, one for each machine, individual circuit connections from predetermined ones of the secondary sources of current through the medium of said electronic valves to said magnets and means responsive to the carrier currents for completing said circuit connections in accordance with agreement of the phases of the carrier currents with the phases of the currents of the connected secondary sources to energize the printing control magnets, whereby the different sets of control contacts of the machines at the first mentioned end of the line may be operated simultaneously by their individual operating means to effect control of the energization of printing control magnets of the machines at the other end of the line to effect printing according to the preselected code.

2. In a communication system comprising a plurality of printing telegraph machines at each end of a common line, in combination, means at one end of said line comprising a phase transformer having a plurality of sets of secondary the first mentioned end of the line by their inditaps for supplying currents at different phases, vidual operating means, energization of printing a wave form modifying device for each of said control magnets of the machines at the other currents, a plurality of sets of control contacts, end of the line is controlled to effect printing acone set for each machine, including a series of cording to the preselected code.

normally open contacts and a normally closed 3. A communication system comprising a plu contact, individual operating means for immerality of units at one end of a line, a transmiti diately opening the normally closed contact and ting device for each unit including a plurality for closing the normally open contacts at a difof control contacts for normally transmitting a ferent-ial time according to a preselected code, 1 carrier current of a predetermined phase differand circuit connections normally completed by ent from the carrier current of the other units, the normally. closed contacts and then completed individual means for operating the contacts of under control of the normally open contacts as each transmitting device so as to interrupt said the latter contacts are operated, from predetercarrier current in accordance with a preselected mined ones of said sets of secondary taps through code to establish impulse representing characthe related wave form modifying means to the ters, a receiving device for each unit normally line to impress modified wave forms of carrier responsive to impulses of a predetermined phase currents on said line of predetermined difierent different from the phase of the current normally phases to represent the different machines; and transmitted by said units, a plurality of similar means at the other end of the common line comunits at the other end of the line, each unit havprising a phase transformer having a plurality ing a receiving device responsivelymatched in of sets of secondary taps for supplying current phase with a predetermined one of the firstat difierent phases corresponding to the phases named units and a transmitting device for sendof the current from the first mentioned transing out carrier current on the line to which a former, an electronic valve connected to each predetermined one of the receiving devices of the of the sets of taps of the second mentioned transfirst-named units is responslvely matched in former, a plurality of printing control magnets, phase, whereby the various units at either end one for each machine, individual circuit connecof the line may transmit to or receive character tions from predetermined ones of the sets, of impulses from the matched units at the other taps of the second mentioned transformer end of the line over the said line without interthrough the medium of said electronic valves to ference, and switching means associated with said magnets, and means responsive to the careach unit and controlled by the operating means rier currents for completing said circuit connecfor the transmitting control contacts of said unit tions in accordance with agreement of the phases upon operation thereof for switching the receivof the carrier currents with the phases of the log means of said unit from current of the norcurrents of the connected taps of the second mal receiving phase to current of the normal mentioned transformer to energize the printing sendingphase.

control magnets.whereby,upon operationthenor- CHARLES R. DOTY. mally open control contactsof the machines at 

